1. Field of the Invention
This invention relates to the production of a synthesis gas by a reaction of a carbonaceous material with oxygen, oxygen enriched air or air and steam at elevated temperatures.
When oxygen is used in a purity range above 90 volume percent, the synthesis gas is rich in carbon monoxide and hydrogen and is an excellent feed material for the synthesis of various chemicals such as, for example, ammonia, methanol and various hydrocarbons. On the other hand, if air or oxygen enriched air is used then the synthesis gas is dilluted with nitrogen contained in the air and the synthesis gas becomes a fuel gas.
2. Prior Practice
A number of processes, for example, the Koppers-Totzek Process produce synthesis gases from carbonaceous material. A typical process involves the gasification of coal by the reaction of coal with oxygen and water vapor at elevated temperatures. The resulting gas generally consists of two predominant components; carbon monoxide and hydrogen. The ratio which these two components bear to each other depends upon factors such as the gasification process employed, the kind of carbonaceous material, and the relative ratios of the coal and oxygen and steam used. Attempts are made to adjust the ratio of these constituents in the resulting gas to the ultimate desired for the particular use to be made of the gas.
In the coal gasification process, as exemplified for example by the Koppers-Totzek Process, a mixture of the finely pulverized fuel, steam and oxygen is fed into the reactor where, at a high temperature, the reaction of the ingredients of the mixture is almost instantaneous to produce the gas. The gas discharges from the top and most of the ash from the coal becomes a fluid slag and flows from the bottom of the reactor. Although the reaction from the ultimate standpoint appears simple and to take place almost instantaneously, it is postulated that two reactions take place. Some of the carbon of the coal reacts exothermically with the oxygen to provide the quality of heat to raise the temperature of the reacting mass to such a degree that the rest of the carbon can be reacted endothermically with the steam to produce carbon monoxide and hydrogen. The ratios of the fuel, oxygen and steam to be used can be varied to an extent to obtain a desired final gas composition, but it is appreciated that inasmuch as these are fed together as a mixture into the reactor it is difficult to change the individual constituents to any great degree. If a less pure oxygen such as oxygen-enriched air or air alone be used, the accompanying inert nitrogen dilutes the reaction mass. The presence of the diluent uses considerable amounts of energy, tending to consume more coal in bringing the reaction mass to the reaction temperature and dilute the final gas composition as far as such may be reflected in its Btu content or usable constituents such as the carbon monoxide and hydrogen. If either oxygen stream were preheated wtih gasifier hot synthesis gas then the coal usage would be lowered and the gasifier synthesis gas quality would be improved as regards to the production of carbon monoxide and hydrogen because the carbon dioxide level would be reduced since a lower quantity of exothermic heat would be required for the reaction.